Wireless security systems include one or more sensor-transmitter units, placed remotely throughout the premises, that communicate with a system controller. The sensors monitor various conditions that may constitute a threat to security, such as fire, smoke, glass breakage, motion, forced entry, or other conditions. The transmitters send operating signals to the system controller, conveying information as to status or conditions at the sensor-transmitter. For example, when a sensor detects a security condition, its corresponding transmitter sends an alarm signal to the system controller.
The system controller is typically mounted on a circuit board and enclosed by a metal box or casing. This physical manifestation and arrangement of the system controller is often called the control panel. The control panel is usually placed in a relatively interior location on the premises such as the basement or a closet.
The system controller interprets the operating signals, including alarm signals, sent by the sensor-transmitter units. For example, in response to an alarm signal, the system controller may send an alarm notification message via a telecommunications link such as the local telephone network, to a central station, whereby the police, fire department, or other appropriate agency is notified.
Another type of operating signal transmitted by the transmitters in the wireless security system is a supervisory signal, indicating to the system controller that the sensor-transmitter unit continues to be operable. In response to the supervisory signal, the system controller can notify the security system user if and when a sensor-transmitter unit is not functioning, so that the user can take corrective action to prevent an undetected breach of security in the future.
The system controller includes one or more antennas, for the reception of operating signals transmitted to it by the transmitters. The antennas are essential to the proper operation of the security system. If a transmitter sends a message indicating an alarm or other change of condition, the message must be received by the system controller. An antenna is necessary for such reception. The antenna converts the operating signal sent by the transmitter, from an electromagnetic wave propagating through the atmosphere into an electrical signal recognizable by a receiver.
One antenna alone is sometimes sufficient for the system controller to receive properly a signal from a transmitter. However, sometimes a signal cannot be received at a particular point in space because it is nullified or cancelled at that point, for example by another signal or by the effects of multipath distortion due to signal scattering in the local premise. The likelihood of proper signal reception by the system controller may be enhanced by utilizing two or more antennas, spaced apart from one another in such a manner as to create multiple points of possible reception, or spatial diversity. In such a spatial diversity receiver system, if a signal is cancelled at the location of one particular antenna, the signal could be received by another antenna at a different location.